Novak Djokovic of Serbia is moving up the list of tennis greats after his fourth Australian Open title. / Lucas Dawson, Getty Images

by Douglas Robson, Special for USA TODAY Sports

by Douglas Robson, Special for USA TODAY Sports

MELBOURNE, Australia - Novak Djokovic's 6-7 (2-7), 7-6 (7-3), 6-3, 6-2 victory Sunday against Andy Murray brought to a close the season's first major. What has the Australian Open taught us? Six observations:

1. Djokovic now one of the greats

With his sixth major and Open-era tying fourth at the Australian Open, Novak Djokovic joins the likes of Boris Becker and Stefan Edberg on the Grand Slam leaderboard. Better company awaits.

Like Rafael Nadal and Roger Federer, the Serb is a threat to win on every surface, and he is superior on hardcourts, the surface on which two of the four majors are played. Since the start of 2011, he has captured five of nine Slams.

At 25, and with a good five years of prime playing ahead of him, double-digit majors are well within reach.

"It's very realistic," said his coach, Marian Vajda. "I can clearly say that his mental state is fantastic now, he's very confident and rolling."

The 2012 French Open runner-up has yet to conquer Paris, but with Rafael Nadal coming back from an extended absence, this could be his year, too.

2. Azarenka is a tough cookie

By beating resurgent Li Na to win her second consecutive title in Melbourne, Victoria Azarenka kept her grip on No. 1. And she showed she could get the job done in difficult circumstances.

After questionable use of a medical timeout in her semifinal win against American teenager Sloane Stephens, she locked in and metaphorically donned the hoodie and headphones she prefers when she takes the court.

She blocked out a tough opponent, an unfriendly crowd, two days of savage treatment in the press and social media and managed to win the tournament without her best stuff.

Her mental fortitude? Intact.

"I know how tough she is," said her coach, Sam Sumyk. "I've known that a long time."

3. Murray should contend for No. 1

Andy Murray has reached the final of the last three majors, won the U.S. Open and pocketed an Olympic gold medal. Is there any question he's a formidable member of the Big Four?

Under Ivan Lendl's tutelage, the 25-year-old Scot has improved his court management, mixing in offensive strikes with his smothering defense. Verbally self-abusive, he has improved his body language and emotional comportment.

In his five-set win against Federer, he absorbed the 17-time major champion's directed anger and was the picture of Zen in the final set after blowing a chance to serve it out in the fourth set.

"He neutralized Federer's mindset by being calm, which is really cool to see," said EuroSport commentator Mats Wilander. "He is learning fast."

At this rate, he is a bona fide contender for the No. 1 ranking.

4. Defense rules

Equipment advances, bigger balls and slower courts have created an era of defensive magicians, but Murray, Djokovic and the absent Nadal have pushed retorts to new heights.

They were at it again on Rod Laver Arena on Sunday night, sneakers squeaking as they picked up balls up from their toes at the baseline and launched zingers from full stretch.

With few exceptions such as Roger Federer - and even his game is somewhat of a relic these days - offense is increasingly a losing proposition against the best defenders.

"When he's on defense he can actually win the point with one shot," Andre Agassi said of Djokovic. "That's an evolution of the game."

5. Is it getting too physical?

Serena Williams sprained her ankle; Azarenka tweaked her knee. On Sunday night in the men's, Murray was hampered by a blister.

Li Na? She fell not once but twice in the women's championship match, whacking her head on the Plexicushion surface and blacking out for a a couple of seconds.

Injuries are the normal hazards of elite competition, but the torque and force being inflicted on bodies - not to mention the increasing length of points and matches - is reaching dangerous levels.

6. MTO needs review

That being said, the medical timeout rule needs to be tightened.

There was controversy in the last few days of the women's tournament because of Azarenka's double medical timeout at a crucial time in her match against Stephens.

Tournament officials were clear that Azarenka was within the rules. But legit or not, it's up to officials to make sure the rule is not abused, and most were left with a bad feeling after Azarenka - who had just failed on five match points - was able to recover her composure.

"It's definitely a situation that warrants a review based on controversy it created," WTA CEO Stacey Allaster said.